Generally, an automatic transmission is realized by a combination of a plurality of planetary gear sets, and functions to transfer a rotational power transferred from a torque converter, to an output shaft, by automatically shifting a speed to multiple stages.
In the automatic transmission, the more shift stages are realized, the more appropriate transmission gear ratios may be designed and the more it is possible to realize a vehicle which is excellent in terms of power performance and fuel economy. Therefore, researches have been continuously conducted to realize an increased number of shift stages.
Even if the same shift stages are realized, the automatic transmission has a different operation mechanism depending on a connection scheme of rotation elements (a sun gear, a planetary carrier and a ring gear).
In the meantime, in the automatic transmission, while a plurality of shift stages are realized, an operating condition in which one friction member is released and another friction member is operated when making a shift to a neighboring shift stage should be satisfied from the viewpoint of transmission control.
A background art of the present disclosure is disclosed in Korean Unexamined Patent Publication No. 2008-0033789 (published on Apr. 17, 2008 and entitled “9-speed gear train of automatic transmission for vehicle”).